Nokia N81 - Manual (Page 99)

Applications
99
2 In the first Unit field, select the unit from which you
want to convert. In the next Unit field, select the unit
to which you want to convert.
3 In the first Amount field, enter the value you want to
convert. The other Amount field changes automatically
to show the converted value.
Set base currency and exchange rates
Select Type > Currency > Options > Currency rates .
Before you can make currency conversions, you must select
a base currency and add exchange rates. The rate of the
base currency is always 1.
Note: When you change base currency, you must
enter new exchange rates because all previously set
exchange rates are cleared.